Removal of sulfur compounds from gas streams has been of considerable importance in the past and is even more so today due to environmental considerations. Gas effluent from the combustion of organic materials, such as coal, almost always contain sulfur compounds and sulfur removal processes have concentrated on removing hydrogen sulfide since it has been considered a significant health hazard and because it is corrosive, particularly when water is present. With increasing emphasis on eliminating or minimizing sulfur discharge to the atmosphere, attention is turning to the removal of other sulfur compounds from gas streams.
The process of the present invention provides a new and effective means for the removal of sulfur compounds from gas streams and is particularly effective in the removal of sulfur compounds from natural gas streams.
Numerous natural gas wells produce what is called in the industry "sour gas." "Sour gas" is natural gas that contains hydrogen sulfide, mercaptans, sulfides and disulfides in concentrations that make its use unacceptable. Considerable effort has been expended to find an effective and cost efficient means to remove these objectionable sulfur compounds from natural gas.
A number of processes are available for removal of H.sub.2 S from natural gas streams. Processes presently available can be categorized as those based on physical absorption, solid adsorption, or chemical reaction. Physical absorption processes suffer from the fact that they frequently encounter difficulty in reaching the low concentrations of H.sub.2 S required in the sweetened gas stream. Solid bed adsorption processes suffer from the fact that they are generally restricted to low concentrations of H.sub.2 S in the entering sour gas stream. Chemically reacting processes in general are able to meet sweet gas H.sub.2 S concentrations with little difficulty, however, they suffer from the fact that a material that will react satisfactorily with H.sub.2 S will also react with CO.sub.2. Above all, the processes presently available do not efficiently provide for removal of mercaptans, sulfides and disulfides.
An example of a chemically reactive process is the ferric oxide fixed bed process, wherein the reactive entity is ferric oxide impregnated on an inert carrier. This process is good for the removal of H.sub.2 S but does not appreciably remove mercaptans or other sulfur compounds. The bed can be regenerated, however, the number of regenerations is limited by the build-up of elemental sulfur upon the bed.
A widely used process for removing H.sub.2 S from natural gas depends upon the reactivity of H.sub.2 S with amino nitrogen, see for example U.S. Pat. No. 1,783,901. In recent years several other patents have been granted covering similar compounds. The amine-like chemical compounds currently being employed for removal of H.sub.2 S from gas streams include: monoethanolamine, 2-(2-aminoethoxy)ethanol and diethanolamine. While effective for removal of H.sub.2 S, these compounds do not effectively remove mercaptans, sulfides or disulfides. Installation costs are high and operating costs are high due to substantial energy requirements.
The Shell Oil Company "Sulfinol" process involves both a physical solvent and a chemically reactive agent in the sweetening solution. The physical solvent involved is tetrahydrothiophene 1,1-dioxide and the amine is normally diisopropylamine. This process suffers from the disadvantage that the physical solvent has a high absorption capacity for the hydrocarbon gas constituents and the cost per unit is excessive.
In general, amine type sweetening processes tend to encounter the same kinds of operating problems, which can be roughly categorized as (a) solution loss, (b) foaming and (c) corrosion. In the presence of water H.sub.2 S is corrosive, thus, elimination of corrosion in an amine sweetening unit is all but impossible because most amine type solvents are used in water solution.
Activated carbon and molecular sieves are well-known, however, absorption capacities are limited. Regeneration is possible but this requires sophisticated instrumentation and controls in addition to high energy requirements.
U.S. Pat. No. 4,035,474 discloses a method for removal of sulfur from tail gas by use of a cold bed absorption process. This process utilizes a catalyst, however, catalyst deactivation occurs after 18 hours and a backup unit must be brought on stream while the spent catalyst is regenerated for 12 to 14 hours at 700.degree. F./370.degree. C.
There is an apparent need for an efficient, low-cost gas sweetening process which would remove sulfur compounds from a gas stream effectively and economically. The process of the present invention accomplishes effective and economical removal of sulfur compounds from a gas stream through use of sulfonamide compounds and resins containing pendant sulfonamide functionalities.
The reaction of alkali metal salts of sulfonamides with sulfur compounds is known. For example, a kinetic study of the reaction between sulfides and N-sodium-N-chloro-paratoluene sulfonamide is reported in the Bull. Chemical Society Japan, V.42, 2631 (1969), K. Tsujihara, et al. From the mechanistic study of this reaction, a procedure for the synthesis of sulfilimines was devised.
A procedure is disclosed in U.S. Pat. No. 3,756,976 which removes objectionable thiol odor from polymer latex through the use of numerous compounds that convert the odorous sulfur compounds to a nonodorous form. Specifically claimed is the use of the alkali metal salts of N-halogenated arylsulfonamides. U.S. Pat. No. 3,756,976 teaches the use of these compounds to convert the sulfur compounds to a nonodorous form and not the removal thereof. The disclosed process has the converted sulfur compounds within the polymer latex system and does not teach or suggest that sulfur compounds can be removed from a gas stream through use of the alkali metal salts of N-halogenated sulfonamides.
The reaction of sulfides with salts of N-chloroarenesulfonamides was the first method to be discovered for preparing sulfilimines. Gilchrist et al, Chem. Rev., Vol. 77, No. 3, page 409, 1977.
The reaction of Chloramine-T (trade name for N-sodium-N-chloro paratoluene sulfonamide) with thiols, disulfides, sulfides, sulfoxides and sulfones was reported by D. K. Padma et al, in Int. J. Sulfur Chem., Part A 1971, 1(4), 243-50 and titrimetric determination of mercaptans with chloramine-T is reported by R. C. Paul et al. in Talanta, 1975, 22(3), 311-12. All the references cited do not suggest or disclose that salts of sulfonamides such as chloramine-T can be used to remove sulfur compounds from a gas stream.
It is the novel and nonobvious use of alkali metal salts of sulfonamides and resins containing sulfonamide functionalities in a process to remove sulfur compounds from a gas stream that comprises the present invention.